Variable resistance device



June 17, 1958 C. R. DICKINSON EIAL VARIABLE RESISTANCE DEVICE 2Sheets-Sheet 1 v Filed Oct. 13, 1953 ATTORNEY June 17, 1958 c. R.DICKINSON In Al. 2,

VARIABLE RESISTANCE DEVICE 2 Sheets-Sheet 2 Filed Oct. 15, 153

INVENTORS Mam W/KM? ATTORNEY 2,839,642 Patented June 17, 1958 VARIABLERESISTANCE DEVICE Clarence R. Dickinson, Greene tale, and Bernhard F.Tellkamp, M'ushego, Wis., assignors to Allemlirndiey Conrpany,Milwaukee, Wis., a corporation of Wisconsin Application October 13,1953, Serial No. 385,848

5 Claims. (Cl. 201-45 This invention relates to variable resistanceapparatus such as may be employed as a rheostat or potentiometer and itmore specifically resides in an apparatus having a base upon which isexposed a layer of resistance material that forms a partial circle toprovide a resistance track and a layer of conducting material to providea collector track with brush engaging surface areas substantiallyconcentric with said resistance track, which resistance and collectortracks are electrically bridged by a conducting brush rotatable about anaxis substantially concentric with said resistance track havingcollector engaging portions in sliding contact with said collector trackand a resistance engaging portion in sliding contact with saidresistance which engaging portions define a base area for said brushthat is intersected by the axis of rotation.

It is an object of this invention to provide a variable resistanceapparatus with a resistance track and a collector track with exposedbrush engaging surfaces confined within a circular area of extremelysmall diameter lending the apparatus to miniaturization desirable foruse in complex circuit networks having a great multiplicity ofcomponents compacted within confined space limitations.

it is another object of this invention to provide a variable resistanceapparatus with a rotatable conducting am known as integrally moldedresistors of Which Certain brush bridging resistance and collectortracks having contacting portions in sliding engagement with the tracksthat define a base area intersected by the center of rotation of thebrush to permit a reduction of overall dimension.

It is another object of this invention to provide a variable resistanceapparatus with an operating shaft mounting a brush carrier that extendsfrom the carrier in a direction opposite that of the resistance andcollector tracks, whereby the base supporting the resistance andcollector tracks may have a solid transverse cross section.

It is another object of this invention to provide a variable resistanceapparatus in which a seal may be placed about the operating shaft andhoused within the interior of the apparatus to protect the same andpromote long life for the seal.

It is another object of this invention to provide a variable resistanceapparatus with a minimum of metallic material in close association withconducting elements of the apparatus to reduce the possible leakagepaths to a minimum.

These and other objects and advantages of this invention will appear inthe description to follow. In the description, reference is made to theaccompanying drawings, which form a part hereof, and in which there isshown by way of illustration and not of limitation a specific form inwhich this invention may be embodied.

In the drawings:

Fig. 1 is a side view in elevation and in section of a variableresistance apparatus mounted upon a panel in which this invention isembodied,

Fig. 2 is a view in elevation and in section of the apparatus viewedthrough the plane 22 indicated in Fig. 1.

Fig. 3 is a fragmentary view in section of the brush carrier andoperating shaft forming a part of the apparatus viewed through the plane33 indicated in Fig. 2,

Fig. 4 is a view in elevation and in section of the apparatus shownthrough the plane 44 indicated in Fig. 1,

Fig. 5 is a rear view in elevation of the apparatus shown in Fig. 1,

Fig. 6 is an exploded view in perspective of portions of the apparatus,

Fig. 7 is a view in perspective of a heat extracting insert forming apart of the apparatus, and

Fig. 8 is a side view in elevation of a terminal lead as is employed inthe apparatus.

Referring now to the drawings, there is shown a molded base 1 ofinsulating material having a circular front face 2 that is clearly shownin Fig. 6. Embedded within the base 1 and exposed flush with the face 2is a circular resistance track 3 in the form of a nearly completed ring.The track 3 comprises a shallow layer of conducting material in the formof distributed carbon black particles dispersed within the moldingmaterial of the base 1 to have become an integral portion thereof uponmolding. Substantially concentric with the resistance track 3 is acollector track 4, also exposed flush with the face 2. The track 4covers a circular area at the center of the face 2 and, like the track3, is formed of a plurality of conducting particles molded integrallywithin the base 1 in a shallow layer near the surface. The particlescomprising the collector track 4 are more densely distributed than inthe resistance track 3 to provide a conductin spot area of very smallresistance. Variable resistance apparatus comprising resistance andcollector tracks of conducting particles molded within a base ofinsulating material, such as herein described,

forms have been set fortn and described in the patents to Tellkamp No.2,269,136, dated January 6, 1942, and No. 2,514,682, dated July 11,1950.

A set of three terminal leads 5 are embedded within the base 1 at thetime of molding and are disposed with the embedded end of one inelectrical contact with the collector track 4 and the embedded ends ofthe others in contact with the end portions of the resistance track 3.The configuration of a lead 5 is clearly shown in Fig. 8. The hookshaped end is embedded in the base 1 to be rigidly held in place withthe tip entering into a layer of conducting material that forms one ofthe tracks 3, 4.

The molded base 1 also has embedded therein a metallic heat extractingand housing anchoring insert 6, preferably composed of a metal havinghigh heat conductivity. The insert 6 is in the form of an interruptedcylinder, as is more clearly shown in Fig. 7, with a plurality ofperforations '7 through which the material of the base 1 may flow, uponmolding, to rigidly secure the insert 6 in position. The insert 6 isembedded with its forward edge 8 behind, spaced from but very near theresistance track 3, as shown in Fig. 1, to readily receive heat releasedwithin the resistance track 3 and to conduct the same to the exterior ofthe base 1 for disposal as hereafter described.

As shown in Figs. 1 and 5 the rear of the element 6 is exposed and formsa cylindrical metallic wall adjacent a rearwardly facing ledge extendingpartly around the body 1. A set of attachment ears 9, integral with theelement 6, partly isolated from the main body thereof by deeply indentedfilleted notches 9 flanking the same, projects rearwardly as shown inFig. 7 at the time of molding. A sleeve shaped metallic housing 11,inwardly flanged at its rear and punched to closely surround therearward extension of the base 1 is placed as shown inFig. l, in closecontact with the exposed portion of the insert 6. After being thusassembled, the ears 9 are clinched outwardly and forwardly as showninPigs. 1 and 5, securely holding the housing 11 in place and in contactwith the insert 6 to conduct heat therefrom for dissipation over theentire surface of the housing 11. The ears 9, being set apart from theremainder of the insert 6 by the notches 9', are free to be clinchedagainst the housing ll in spite of inevitable dimensional variations inthe base 1, the insert 6 and the housing 11, without splitting of thebase 1.

At the front, the circular cylindrical housing 13; has a lip 14 fromwhich extends a set of cars 15. A bushing 12 with a circular base 1seats upon the lip 14 and the free ends'of the ears 15 are bent over thebushing base 13 to secure the bushing 12 in position. Extending throughthe bushing 12 is an operating shaft 16 having a knurled end 17 withinthe housing 3.1 that is embedded within a molded brush carrier 155composed of an insulating material. Compressed between the bushing 12and the carrier 13 is a'seal 19 that closely encircles the shaft 16.

As shown in Figs. 1, 2 and 3 the carrier 13 is recessed to receive anelectrically conducting brush 2d of carbon and a pair of bias springs21'. The brush 2i) converges radially to terminate in an apex at theouter end that has a contact toe 22 with a small face area in slidingengagement with the exposed surface of the resistance track 3. The brush2% widens from the apex into a broad inner end from which project a pairof collector engaging toes 23 each having a surface in slidingengagement with the collector track 4. a The three contact toes 22, 23of the brush 2!) define a triangular base area that extends across andincludes the axis of rotation of the operating shaft 16 whch is insubstantial coincidence with the centers of the circular concentrictracks 3, 4. The two contact toes 23 rotate within a restricted radiusconfined to the limits of the spot like area of the collector track 4.The spacing of the toes 23 is, however, considerable to providestability for the brush 2% by providing a substantial dimension of thebrush base area along all radii.

As shown in Fig. 3, the springs 21 rest at their ends against abutments2 3 in the recess in the carrier 18. The intermediate portion. of eachspring 21 bears against the back of the brush it? and is bowed toprovide necessary contact pressure between the brush toes 22, 23 and theexposed surface areas of the "'acks and The use of a plurality ofsprings 21 permits contacting engagement with the curved back of thebrush 20 at more than one point and the spring characteristic obtainedis similar to that of a fiat spring.

The forward portion of the carrier la, in which the shaft end 117 isembedded, comprises a boss 25 of reduced diameter from which extendsradially an integral lug 26 clearly shown in Figs. 4 and 6. Secured tothe base 13 of the bushing 12 is a stop 27 that protrudes into the pathof the lug 26 to limit rotation of the carrier 13 and brush Ztl. Themovement of the brush contact toe 22 Will thus be confined to within thelimits of the resistance track 3. To mount the apparatus on a panel,such as designated by the numeral 23 in Fig. 1, the bushing 12 isinserted within an opening provided in the panel and a nut threadedlyreceived by the bushing is brought up tight against the panel 28 toclamp the panel between the base 13 of the bushing 32 and the nut 29.

Leakage resistance paths and breakdown voltage values are maintained atdesired high levels in the apparatus of this invention. The molded baseof insulating material provides sufficient insulation between theresistance tit) track 3 and collector track 4. The terminal leads 5extending directly to the rear are well spaced from one another and fromthe housing 11, and the side walls of the housing If is spaced from thebase 1 with a substantial gap therebetween to insulate the periphery ofthe resistance track 3. The shaft 16 is extended away from the tracks 3,4 and the conducting brush 2% that is seated within the carrier 18, thuseliminating a possibility of insulation breakdown between the shaft 16and the conducting elements of the apparatus.

With the shaft 16 disposed entirely to one side of the base 1 thediameter of the base may be reduced from that otherwise necessary if theshaft 16 were extended through a central opening in the base. Withelimination of a central opening in the base the collector track 4 isreduced to a spot area and the brush 2% is disposed with the contactingtoes defining an area encompassing the axis ofrotation. The resistancebetween the lead embedded in the collector track 4 and the brush toes 23will be very small and will be a nearly constant value over the entirerange of brush rotation. As the brush is rotated about an axisintersected by the brush base area one of the collector contacting toes23 will move toward the lead end embedded in the track 3 and the othertoe 23 will recede. This movement tends to retain the resistance of thecollector track 4 nearly constant. In the event the embedded lead end isconcentric with the brush axis, then the geometry will remain the sameregardless of rotation.

We claim:

1. In a variable resistance apparatus the combination of a base having afront face with an arcuate resistance track, side faces extendingrearwardly from the front face, and an extension rearward of said sidefaces that has sidewardly facing orientating walls set back from saidside faces to form a rearwardly facing ledge; a cover formed of a thinmetallic sleeve that is flanged inwardly at the rear with inner edges ofthe flanging closely conforming with said orientating walls, said coverencircling said base with the flanging seated upon said ledge andpositioned by the conformance of said fianging inner edges with saidorientating walls whereby the inner surface of said sleeve extendsforwardly from the ledge at a predetermined spaced distance from saidside faces of said base to present a gap therebetween; clamping means onsaid base holding said fianging against said ledge; a shaft supportingmember to the front of said base mounted on said cover; and an operatingshaft assembly borne by said shaft supporting member including a slidingcontact bearing upon said resistance track.

2. In a variable resistance apparatus the combination of a moldedinsulating base having a front face with an arcuate resistance track andside faces extending rearwardly from the front face; a metallic heatconductive arcuate insert embedded in said base to the rear of saidresistance track with exposed side walls set back from the side faces ofsaid base to form a ledge at the rear of the base and having a pluralityof attachment ears extending therefrom; a cover formed of a thinmetallic sleeve that is flanged inwardly at the rear with inner edges ofthe flanging presenting an opening closely conforming with the exposedside walls of said insert, said cover encircling said base with theflanging seated upon said ledge and positioned by the conformance ofsaid hanging with the side walls of said insert, and said cover beingheld tightly in position by clinching said attach-- ment ears over thehanging of the cover; a shaft supporting member to the front of saidbase mounted on said cover; and an operating shaft assembly borne bysaid shaft supporting member including a sliding contact bearing uponsaid resistance track.

3. In a variable resistance apparatus the combination of a base assemblyhaving a molded body witha front face presenting an arcuate resistancetrack and side faces extending rearwardly from the front face, and ametallie insert of arcuate configuration partially embedded in themolded body with an edge in close proximity to said resistance track toreceive heat evolved in the track and protruding at the rear of the basewith a set of attachment ears; said base assembly presenting sidewardlyfacing orientating surfaces to the rear of and set back from the sidefaces of the molded body to form a rearwardly facing ledge over whichsaid attachment ears may be turned; a metallic cover formed of a thinsleeve encircling the base that is flanged inwardly at the rear withfianging conforming to the orientating surfaces of the base assembly,which hanging is seated upon said ledge with the attachment earsclinched thereon whereby the cover is retained in predetermined positionboth circumferentially and radially by the conformance of the flangingwith said orientating surfaces such that the inner surfaces of saidsleeve extend forwardly from the ledge at a spaced radial distance fromthe side faces of said molded body; and a sliding contact memberengaging said resistance track mounted at the front of said sleeve.

4. In a variable resistance apparatus the combination of a base having afront face with an arcuate resistance track, rearwardly extending sidefaces, and a rear portion with a ledge comprising rearwardly andsidewardly facing orientating walls; a cover formed of a sleeveencircling said base that has flanging at the rear turning over andseated upon said ledge with close conformance to said orientating wallsthereby retaining the cover and base in fixed relative position with thewalls of the cover spaced from the side faces of the base, and saidcover also having a mounting surface at its front; clamping means onsaid base holding said cover flanging against said ledge; 21 memberincluding a bushing spaced from the front of said base which issupported on said mounting surface of said cover; second clamping meansretaining said member in position on said mounting surface of saidcover; a rotatable operating shaft extending through said bushing to theinterior of said cover; and a brush member within said cover carried bysaid shaft and in engagement with said resistance track.

5. In a variable resistance apparatus the combination comprising ametallic housing having front and after ends; an insulating baseattached to the after end of said housing in fixed relation thereto; anarcuate resistance track carried on the forward side of the base; aconductive collector track radially within the resistance track carriedon the forward side of the base; a metallic arcuate insert embedded insaid base to the rear of said resistance track having exposed clampingportions that engage said housing in heat transferring relation theretoand retain the housing and base in attached, fixed relation; a bushingattached to the forward end of the housing in fixed relation thereto; arotatable operating shaft extending through the bushing with an endwithin the housing sp ced from the forward side of the insulating a; anondcforrnable conductive brush spanning between the resistance andcollector tracks having a contact toe engaging the resistance track anda pair of contacting toes engaging the collector track, said toesdefining a triangular base area encompassing the axis of rotation ofsaid shaft; a brush carrier mounted on said end of said shaft forrotation therewith, which carrier has a cavity that receives said brushfor engaging the sides thereof to impart rotational movement thereto andwhich also has spring receiving recesses disposed to the sides of and incommunication with the cavity; and a transversely deflectable Wirespring interposed between the brush and brush carrier with the endsthereof received in and engaging said recesses and the center portionthereof engaging said brush to urge the brush against said tract-rs andthe carrier toward the bushing.

References *Citetl in the file of this patent UNITED STATES PATENTS2,040,278 Siegel May 12, 1936 2,236,343 Meuer Mar. 25, 1941 2,514,682Tellkamp a- July 11, 1950 FOREIGN PATENTS 684,067 Great Britain Dec. 10,1952

